A conventional optical window is utilized in an electronics enclosure (or a housing) to provide a means of allowing an optical signal from an optical sensing device (e.g., a laser scanner, a digital camera, a CCD device, an IR device, etc.) and a return signal to pass with minimal distortion and loss through an environmentally sealed optical aperture. Such window prevents water, electro-static discharge (“ESD”), dust and moisture from entering the housing thereby protecting sensitive electronics and optical devices contained within. The conventional optical window is assembled into the housing as a secondary operation requiring several parts and several assembly operations.
FIG. 1 shows a conventional assembly 1, which includes a bezel 4, a sealing material (gasket) 8, a window 6 and a housing 2. For a plastic injection-molded housing 2, a mold tool is required for the bezel 4, as well as for the housing 2. Each part is fabricated separately. The bezel 4 is placed over the window 6 and is ultrasonically welded to the housing 2. The bezel 4 fixes the window 6 in place, while the gasket 8 provides the environmental seal.
The above-described method requires a significant number of post-molding operations. The parts must be fabricated, inspected, packaged and transported to the final assembly location. The parts are removed manually by the operator, inspected and cleaned if necessary. The operator places the parts in a nest tool to properly align them for the ultrasonic welding operation. The horn of the ultrasonic welding apparatus must fit into the cavity of the housing in order to apply energy to the parts for welding. After the welding energy is applied, the operator removes the assembly from the fixture and visually inspects it for proper alignment of all parts.
The process results in yield loss and poor reliability. A visual inspection is a poor way to screen for seal defects. For example, a housing 2 with an inadequate seal 8 may escape this screening and there is yield loss as the parts may leak due to improper installation of the gasket 8 or improper functioning of the ultrasonic welding equipment. In addition, the gasket 8 may lose elasticity or adhesion over time, resulting in a leaking housing 2 which is not environmentally sealed.